Motor drives and other power conversion systems convert electrical power from one form to another, and may be employed in a variety of applications such as powering an electric motor using power converted from a single or multiphase AC input source. One common form of motor drive is a current source converter (CSC), in which a rectifier converts input AC power from a single or multiphase AC input source to provide DC current to a DC link circuit. An output inverter converts the DC link current into single or multiphase AC output power to drive a motor load. Such power conversion systems may be subject to both differential and common mode voltages and currents, which can cause a variety of problems including degradation of the power conversion system and/or the motor load. For instance, motors are susceptible to damage or performance degradation caused by appearance of excessive common mode voltages on the motor leads. Previously, low and medium voltage converters often include differential mode inductors as well as common mode control apparatus to address these problems. However, separate differential and common mode devices are costly and occupy space in a power conversion system. Other techniques include modification of switching waveforms in one or both of the rectifier and inverter stages, but such techniques often require complicated switching control systems. Common mode and differential mode noise effects can also be addressed by using isolation transformers within the power conversion system, but these transformers add cost to the system and occupy space. Thus, there remains a need for improved common mode and differential mode suppression apparatus and techniques in power conversion systems.
U.S. Pat. No. 7,164,254 to Kerkman et al., issued Jan. 16, 2007 and assigned to the assignee of the present application discloses common mode voltage reduction techniques in which the switching sequence is modified to avoid using the zero vectors in order to reduce common mode voltages in the motor. The entirety of this patent is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 7,106,025 to Yin et al., issued Sep. 12, 2006 and assigned to the assignee of the present application discloses techniques for canceling dead time effects in the algorithm to reduce common mode voltages produced by a three-phase power conversion device in a rectifier/inverter variable frequency drive (VFD), the entirety of which is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 5,422,619 to Yamaguchi et al., issued Jun. 6, 1995 discloses a common mode choke coil with a couple of U-shaped cores and 4 coils wound around legs of the cores, the entirety of which is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 5,905,642 to Hammond, issued May 18, 1999 discloses a common mode reactor between a DC converter and an AC converter to reduce common mode voltage from current source drives, the entirety of which is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 6,617,814 to Wu et al., issued Sep. 9, 2003 and assigned to the assignee of the present application discloses an integrated DC link choke and method for suppressing common-mode voltage and a motor drive, the entirety of which is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 6,819,070 to Kerkman et al., issued Nov. 16, 2004 and assigned to the assignee of the present application discloses inverter switching control techniques to control reflected voltages in AC motor drives, the entirety of which is hereby incorporated by reference as if fully set forth herein.
U.S. Pat. No. 7,034,501 to Thunes et al., issued Apr. 25, 2007 and assigned to the assignee of the present application discloses gate pulse time interval adjustment techniques for mitigating reflected waves in AC motor drives, the entirety of which is hereby incorporated by reference as if fully set forth herein.